1. Field of the Invention
The present invention relates to a solid-state imaging device including, on top of a substrate, a photoelectric conversion element formed by sandwiching a photoelectric conversion film made of an organic material or an inorganic material by a pair of electrodes. Further, the present invention relates to a method of fabricating the solid-state imaging device, a method of driving the solid-state imaging device, and an electronic apparatus that uses the solid-state imaging device.
2. Description of the Related Art
In the related art, in a solid-state imaging device formed by laminating a photoelectric conversion element made of an organic photoelectric conversion film on top of a semiconductor substrate, the organic photoelectric conversion film is sandwiched by an upper electrode and a lower electrode that are used to apply voltage to the organic photoelectric conversion film. Signal charge generated by the organic photoelectric conversion film is read out by connecting one of the upper electrode and the lower electrode to transistors formed in the substrate (Japanese Unexamined Patent Application Publication No. 2005-268476).
FIGS. 14 and 15 are each a schematic cross-sectional diagram of a solid-state imaging device according to the related art. FIG. 14 shows a solid-state imaging device 100 according to the related art formed by three transistors including an amplifier transistor Trc, a reset transistor Trb, and a select transistor Trd. FIG. 15 shows a solid-state imaging device 101 according to the related art formed by four transistors, with a transfer transistor Tra further added to the structure shown in FIG. 14.
As shown in FIGS. 14 and 15, the solid-state imaging devices 100 and 101 according to the related art have the individual transistors formed in a substrate 102, a wiring layer 104 formed on the substrate 102, and a photoelectric conversion element 109 formed on top of the wiring layer 104. The photoelectric conversion element 109 is formed by laminating a lower electrode 106, an organic photoelectric conversion film 107, and an upper electrode 108 in order on the wiring layer 104. The transistors Tra to Trc each include a source/drain region 113 formed by a high concentration impurity region in the near-surface side of the substrate 102, and a gate electrode 111 formed on the surface of the substrate 102 via a gate insulating film 103. In the wiring layer 104, a plurality of layers of wires 110 are formed so as to be laminated via an interlayer insulating film 105. Connections between desired wires, and between the wires 110 and the substrate 102 are each made through a contact 112.
As shown in FIG. 15, in the case of the solid-state imaging device 101 having four transistors including the transfer transistor Tra, the lower electrode 106 is connected to a P-type or N-type high concentration semiconductor region (source/drain region 113) formed in the substrate 102, via the wiring layer 104. In the solid-state imaging device 101 shown in FIG. 15, signal charge generated by the photoelectric conversion element 109 is connected to a photodiode region PD serving as a source region of the transfer transistor Tra, via the lower electrode 106 and the wiring layer 104, and the signal charge is stored in the source region. Thereafter, by the transfer transistor Tra, the signal charge stored in the photodiode region PD is transferred to a floating diffusion FD serving as a drain region, and a pixel signal is outputted via the amplifier transistor Trc. Also, the potential of the floating diffusion FD is reset by the reset transistor Trb.
On the other hand, as shown in FIG. 14, even in the case where no transfer transistor is formed, and the lower electrode 106 is directly connected to the gate electrode 111 of the amplifier transistor Trc, the lower electrode 106 is connected to the high concentration semiconductor region serving as the source region of the reset transistor Trb.
In this way, in each of the solid-state imaging devices 100 and 101 according to the related art, the lower electrode 106 is connected via the contact 112 to the high concentration semiconductor region formed in the substrate 102, for purposes such as storing the signal charge generated in the organic photoelectric conversion film 107, and resetting the potential of the lower electrode 106.
Incidentally, for typical solid-state imaging devices according to the related art having a photoelectric conversion element inside a semiconductor substrate, in order to suppress dark current produced at the interface of the semiconductor substrate, it is common to form a dark current suppression region to reduce dark current.
However, in the case of the solid-state imaging devices 100 and 101 according to the related art having the photoelectric conversion element 109 made of the organic photoelectric conversion film 107 as described above, it is not possible to form a semiconductor region for reducing dark current at the connecting part (region indicated by a broken line “a”) of the high concentration semiconductor region and the contact 112. Thus, the connecting part becomes the source of dark current. Accordingly, unlike typical solid-state imaging devices having a photoelectric conversion element made of a photodiode inside a semiconductor substrate, the solid-state imaging devices 100 and 101 according to the related art formed by the photoelectric conversion element 109 made of the organic photoelectric conversion film 107 have a problem in that dark current is accumulated even during charge storage.
While the above example is directed to the case of a photoelectric conversion element formed by sandwiching an organic photoelectric conversion film by upper and lower electrodes, the same problem arises also in the case where a photoelectric conversion element formed by sandwiching an inorganic photoelectric conversion film by upper and lower electrodes is provided on top of the substrate.